The retina acting as a photoreceptive tissue is located at the inner surface of the wall of eyeball. When pathologic lesion occurs on the retina, eyesight fails, sometimes resulting in blindness. Such retina is broadly divided into sensory retina and retinal pigment epithelium. Such sensory retina is divided into 9 layers, and comprises visual cells as first neuron, bipolar cells as second neuron, ganglion cells as third neuron, and other cells (Hyojun Ganka Gaku, 7th edition, pp. 103-107, Igaku-Shoin Ltd., 1998).
Various retinal diseases are developed depending on the causes of diseases or onset forms. Examples of a disease affecting the retinal nerve may include glaucoma, diabetic retinopathy, retinal artery obstruction, retinal venous obstruction, macular degeneration, and retinopathy of prematurity.
It has been considered that the cell death of retinal nerve cells is deeply associated with dysfunction of the retinal nerve. Factors, which contribute the cell death of refinal nerve cells, may include apoptosis, neurotoxicity caused by glutamic acid, the absence of a neurotrophic factor, the abnormality of mitochondria, caspase activation, nitric oxide, and autoimmunity (Atarashii Ganka, 19(7), 903-912, 2002). For example, from the viewpoint of suppression of the cell death with an excitatory neurotransmitter such as glutamic acid, compounds having antagonistic action to N-methyl-D-aspartic acid have been studied (JP-A-8-506807; Scrip No. 2229, p. 13, 1997; Scrip No. 2307, p. 10, 1998).
As stated above, various factors are associated with the cell death of retinal nerve cells. Other than compounds having antagonistic action to N-methyl-D-aspartic acid, compounds useful as remedies for diseases such as glaucoma, diabetic retinopathy, retinal artery obstruction, retinal venous obstruction, macular degeneration, and retinopathy of prematurity, are required.